鳥居なごむによる日本のライトノベル。イラストは鴨居知世が手掛けている。 KAエスマ文庫より刊行された。「異界士」と呼ばれる特殊な能力を有する存在が、「妖夢」と呼ばれる人間に害を及ぼす存在と戦うダークファンタジー作品。第2回京都アニメーション大賞奨励賞受賞作。 ある日、神原秋人は今にも校舎の屋上から飛び降りそうな栗山未来を見つける。それぞれに事情を持つ半妖夢の少年と血に纏わる異界士の少女が出会い、やがて2人は大地主である名瀬家を巻き込んだ事件に関わっていく。
The story is a recap of the TV series "Kyoukai no Kanata". Mirai Kuriyama is the sole survivor of a clan of Spirit World warriors with the power to employ their blood as weapons. As such, Mirai is tasked with hunting down and killing "youmu"—creatures said to be the manifestation of negative human emotions. One day, while deep in thought on the school roof, Mirai comes across Akihito Kanbara, a rare half-breed of youmu in human form. In a panicked state, she plunges her blood saber into him only to realize that he's an immortal being. From then on, the two form an impromptu friendship that revolves around Mirai constantly trying to kill Akihito, in an effort to boost her own wavering confidence as a Spirit World warrior. Eventually, Akihito also manages to convince her to join the Literary Club, which houses two other powerful Spirit World warriors, Hiroomi and Mitsuki Nase. As the group's bond strengthens, however, so does the tenacity of the youmu around them. Their misadventures will soon turn into a fight for survival as the inevitable release of the most powerful youmu, Beyond the Boundary, approaches.
After Akihito Kanbara reunites with Mirai Kuriyama—whom he believed had vanished after defeating Beyond the Boundary—he discovers a heartbreaking fact: Mirai has lost all memory of him, their friends, and her past as a Spirit Warrior. Akihito is utterly devastated, but realizes that she has a unique opportunity. Mirai can finally live the life of a normal girl—where she'll be completely devoid of the supernatural society that both shunned and used her. While it's all for the sake of Mirai's happiness, the price is costly—Akihito and his friends must keep her true origins a secret from her, and as a result avoid befriending her. However, the troubling memories of Mirai's old life gradually begin to resurface, and a mysterious new evil leads a group of shadow-like creatures into the city with the goal of seeking her out. As the situations become dire, Akihito must fight to protect himself, his closest friends, and Mirai—the bespectacled beauty he holds most dear.